Puzzle for the smart guys...
Puzzle for the smart guys... Why is my car slow? I think I might finally have figured it out. When I bought car, I figured I had a 3.73 in rear (car is a WS6 98 model). I figured this based on MPH @ specific RPM's. My 1/4 mile time slips always say 102.5-103 MPH in the 1/4. I am always @ top of 3rd w/ my M6 (sometimes bouncing off stock limiter-6200rpm) at the traps. But I go back today to the tables, and notice that w/ 3.73 @ 102.5mph, the max rpm w/ a 3.73 is like 99mph in 3rd gear (given my stock tire size of 275/40-17). Therfore, I now think there must be slippage b/w the crank and rear wheels. So my hypothesis is that I really have a stock 3.42 gear which is slipping @ the clutch and therfore appearing as though I have a 3.73. Either that or 1. my tach is incorrect or 2. the track's computer is wrong on the mph in the traps. What do you think...could a slipping clutch cause this?
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You can all so jack the rear of the car and rotate the tire one revolution and count the turns of the drive shaft with 3:73's it will rotate 3-3/4 times and with 4:42's it will rotate almost 3-1/2 times
If it was slipping bad enough to slip at the top of 3rd at 100 mph, it would be slipping under higher loads, like under WOT in 1st and 2nd. Thats where you would feel it first.
+1 on jack it up and spin the tire around 1 time.
+1 on jack it up and spin the tire around 1 time.
You can't figure out what gears you have from your speedometer if the pcm wasn't programmed for the new gear ratio. So you're not really calculating what gears you have, you're calculating the value the pcm thinks you have.
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dddd True, but the time slip gives me my mph as well and doesn't need re-calibration due to whatever gear I have.
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I don't think you have a slipping clutch, I think you should use a handheld GPS to find out how fast you are really going, The tachs on these cars are slow moving (hence the reason they are not real accurate when racing) but for just showing cruise RPM they are quite accurate. Check your speed multiple times with a GPS while on flat ground in 4th gear @ a steady 3,000 RPM. I think you have 3.42's 
It isn't a slipping clutch, I've been there, done that. If it were slipping through the traps @ 100mph, it would slip just going up a slight incline, or accelerating hard from a stop. Burn baby burn! I also think you have 3.42's... Mine did, and with 4.10's and 25.5" tall MT ET street radials, I'm almost to the rev limiter in 4th gear doing 112. Before the turbo of course.
